Shifting sleeves are incorporated into tubulars, such as casing and completion strings. Generally the sleeves are fit to a tool for selectively opening ports through the casing during wellbore completion operations. Typically completion tools, including a shifting tool, are run into the wellbore and located at the sleeve. The shifting tools engaged the sleeve and an axial actuating force is applied to the sleeve to shift the sleeve. The sleeve is initially restrained to the casing using shear screws. The actuating force overcomes the shear screws and is released to move downhole, shifting the sleeve to the actuated position. The movement of the sleeve is arrested by a mechanical stop between the sleeve and the casing.
The initiation and arresting of the movement of sleeve create sufficient forces to damage the sleeve, the shifting tool, and even the cased wellbore environment. It has been observed that the impact force as the sleeve reaches the stop is sufficient to cause a variety of damage. For example, where the shifting tool engages the sleeve using anchors, slips having teeth, wickers or the like thereon, can significantly damage the inside surface of the sleeve when subjected to such actuation forces. When the sleeve suddenly stops, the inertia in the moving components, such as the shifting tool and supporting string, results in large forces at the slip/sleeve interface. Damage results, detrimental to the integrity of the related components and environment including the sleeve, the shifting tool, the downhole tool incorporating the sleeve and the near wellbore.
With reference to FIGS. 1A and 1B, a conventional prior art, resettable sealing device 10 is shown with an anchor comprising button-type slip inserts 12. The resettable sealing device 10 was positioned in a prior art sleeve 14 fit to a prior art sleeve sub, which was in turn incorporated in a casing. Other types of slips 13 having alternate forms of slip inserts or wickers formed thereon were also tested. To test the energy of sleeve actuation, the resettable sealing device 10 was anchored within the sleeve and accelerometers were positioned on casing for detecting the shock resulting from the shifting of the sleeve. The resettable sealing device 10 was actuated by the cone 15 driving slips 13 outwardly to engage inserts 12 onto the sleeve 14. Pressure at the resettable sealing device was increased to impart an actuating force on the sleeve, shearing shear screws, and shifting the sleeve to an actuated position. The movement of the sleeve was arrested against a stop shoulder in the sleeve sub.
As shown in the diagrammatic representation of actual photographs set forth in FIGS. 2 and 3, the sudden stop of the sleeve and device 10 resulted in significant loads therebetween. As shown, the forces caused the inserts 12 to bite further into the inner surface of the sleeve, leaving crescent shaped cuts 18 in the inner wall of the sleeve 14. Subsequent sleeve re-engagement is compromised. Further, the high impact to the sleeve also caused failure of the anchor in some tests including to the slips and slips retaining structure.
Some prior art sleeve shifting systems appear to be purposefully designed to create very high arresting forces resulting in positive indications of sleeve actuation that can be verified at surface. Such systems are particularly at risk of damaging the sleeves and completion tools as a result. Further, there are concerns that the shock loading can result in shock damage to the wellbore environment including the zonal isolation cement and even the formation therebeyond.
Therefore, there is a need for a method for lessening the shock loading during sleeve actuation so as minimize the risk of damaging the downhole apparatus and wellbore during wellbore completion operations.